Pathways leading to formation of surface membrane-bound IgG ("Ig-mem") or to secretion of IgG1 in a cloned, murine myeloma cell line (MOPC-21) are being analyzed. The Ig-mem and secreted IgG1 appear to be separate end-products derived from a common intracellular precursor. Techniques developed for identifying intermediates and end-products of each pathway are being applied to analysis of mous B-lymphocyte differentiation during normal, secondary humoral immune responses. The objective is to determine whether normal IgG1 memory cells exist which integrate IgG1 into surface membrane. The functioning of surface IgG1 on such memory cells as a specific antigen-sensitive receptor will be examined. The effects of specific elimination of such cells will be assessed in terms of its usefulness as a strategy for regulation of the humoral immune response.